1. Field of the Invention
The present invention relates to a composition which, when applied to the surface of a member, can highly hydrophilify the surface of the member and, in addition, can maintain the hydrophilicity. More particularly, the present invention relates to a composition which can highly hydrophilify the surface of mirrors, glass, lenses, and other members to prevent fogging of the surface of the articles or members and the formation of water droplets on the surface of the members or to clean the surface of the members or to accelerate removal of water droplets from the surface of the members by vaporization, thereby rapidly drying the surface of the articles or members.
2. Background Art
Windshields or windowpanes for automobiles and other vehicles, windowpanes for buildings, eyeglass lenses, and cover glasses for various instrument boards, when exposed to cold weather, are often fogged by moisture condensate. Further, bathroom or lavatory mirrors and eyeglass lenses are frequently fogged by steam. Exposure of the surface of an article to a temperature below the dew point of an atmosphere causes the moisture in the atmosphere to condense on the surface of the article and to grow into water droplets, creating a fog on the surface thereof. When condensed water droplets are very small with the diameter thereof being about half the wavelength of visible light, the water droplets scatter light, apparently rendering the glass and the mirror opaque, which also results in lost visibility.
Further progress of condensation of the moisture to thereby cause fine condensed water droplets to unite and grow into larger discrete water droplets brings about refraction of light in the interface of the water droplets and the surface of the article and in the interface of the water droplets and the air, causing clouding, blurring, creation of a spot pattern or otherwise fogging on the surface of the article. Consequently, in the case of a transparent article, such as glass, a see-through image is distorted, causing lowered see-through, while in the case of a mirror, a reflected image is disturbed.
Further, exposure of windshields or windowpanes for vehicles, windowpanes for buildings, rearview mirrors for vehicles, eyeglass lenses, and shields for masks or helmets to rainfall or a spray of water to thereby cause a large number of discrete water droplets to adhere onto the surface brings about clouding, blurring, creation of a spot pattern or otherwise fogging on the surface, which, here again, results in lost visibility.
It is needless to say that the "fogging or clouding" has a great effect on the safety and the efficiency of various works. For example, fogging or clouding of windshields or windowpanes of vehicles and rearview mirrors of vehicles in cold weather or rainy weather makes it difficult to ensure the field of vision and, hence, is detrimental to traffic safety for vehicles. Fogging of endoscopic lenses, dental mirrors, and converging lenses for laser dental treatment equipment will place an obstacle on proper diagnosis, operation, and treatment. Fogging of cover glasses for instrument boards renders reading of data difficult.
On the other hand, in the field of buildings and coatings, the pollution of the environment has posed a problem of contamination of exterior materials for buildings, outdoor buildings, and coatings provided thereon. Dust and particles floating in the air deposit on the roof and the outer wall of buildings in fine weather. Upon exposure to rainfall, the deposits flow together with rainwater and flow down along the outer wall of the building. Further, in rainy weather, suspended dust is carried by rain and flows down on the outer wall of the surface of the building and the surface of the outdoor building. As a result, the contaminant adheres along the course of the rainwater. As the surface dries, soil appears in a stripe pattern.
Combustion products, such as carbon black, municipal dust, and contaminants of inorganic materials, such as clay particles, constitute the soil on the coating of the exterior material for the building. Such a wide variety of contaminants are considered to render measures for antifouling complicate (Yoshinori Kitsutaka, "Gaiheki Shiage Zairyou No Osen No Sokushin Shiken Houhou (Accelerated Testing Method for Contamination of Finish Materials of Outer Wall)", Journal of Structural and Construction Engineering (Transactions of AIJ), No. 404, October 1989, pp. 15-24).
The use of a water-repellent paint, such as polytetrafluoroethylene (PTFE), has hitherto been considered preferable for preventing the exterior of the building and the like from being soiled. In recent years, however, that the surface of the coating is made hydrophilic as much as possible has become recognized as more effective for municipal dust containing a large amount of a hydrophobic component (Kobunshi, Vol. 44, May 1995. p. 307). Accordingly, coating of buildings with a hydrophilic graft polymer has been proposed in a newspaper ("Japan Chemical Week", January 30, 1995). According to this report, the coating has a hydrophilicity of 30 to 40.degree. in terms of contact angle thereof with water.
Inorganic dust typified by clay minerals has a contact angle thereof with water of 20.degree. to 50.degree. and, hence, has affinity for the graft polymer having a contact angle thereof with water of 30.degree. to 40.degree. and is likely to adhere on the surface of the graft polymer. Therefore, it is considered that the coating of the graft polymer cannot satisfactorily prevent soiling with inorganic dust.